Recovery of naphthenic acids



Oct. 1954 M. FAINMAN ET AL 2,692,280

RECOVERY OF NAPHTHENIC ACIDS Filed Dec. 20, 1951 2 Sheets-Sheet l A-Saap-il "A" 80 I Percenfage Wafer Separated In Ten Minutes from Diluted Soap-Oil -H Systems Containing Varied Percentages of H 50 E 60 E Soap-Oil "B" 4.1 50 Q Q 40 STO/CH/OMETR/C QUANTITY OF H 80 EMPLOYED i INVENTORS: Morfon Fainman F, glorman E. Lemmon g r w. L'erf a AITORN; Y

Oct. 19, 1954 M. FAINMAN ET AL 2,692,280

RECOVERY OF NAPHTHENIC ACIDS Filed Dec. 20, 1951 2 Sheets-Sheet 2 Percentage Water Separated in Ten Minutes from Soap-Oil-H 50 Systems Containing 90 80% of the Stoichiometric Quantity of H 80 in Varied Concentrations (13.4 Salt) (19.4 Salt) WATER SEPARATED H 80 CONCENTRATION 4 INVENTORS Morton Fainman Fig. 2 BY %Z7w? 332"" ATTORNEY Patented Oct. 19, 1954 UNITED STATES PATENT OFFICE RECOVERY OF NAPHTHENIC ACIDS Application December 20, 1951, Serial No. 262,624

16 Claims. 1

The present invention relates to an improved process for recovering naphthenic acids from alkali treated oils. In particular it relates to improvements in the recovery of naphthenic acids from heavy bottoms or residues resulting from the distillation of alkali treated lubricating oils.

Naphthenic acids are carboxylic acids of cyclic character having molecular weights in the range of from about 200 to about 500, usually from about 250 to about 400, which occur in and are obtained from petroleum. Treatment of petroleum oils containing such acids with a base, e. g., caustic soda, results in the formation of the basic metal soaps of the acids, or naphthenates, as they are usually referred to. A common source of such naphthenic acids is the residue resulting from the vacuum distillation of an alkali treated lubricating oil fraction of a naphthenic crude. These acids have been recovered by treating such residues with a mineral acid, e. g. sulfuric acid, to regenerate the naphthenic acids. Certain major problems have been encountered, however, in recovering naphthenic acids from such residues, among which have been the development of difiicultly resolvable emulsions which retain substantial amounts of inorganic salt produced in the neutralization reaction and carry same over into subsequent purification equipment and the excessive foaming due to H28 evolution which occurs when the residue contains sulfur in the form of NazS, etc. We have now discovered that the problems of high salt carry-over and foaming may be avoided if certain critical improvements are made in the prior art methods of recovering naphthenic acids from soap-oils, as such naphthenic acid soap containing residues will hereinafter be referred to.

It is an object of the present invention to provide an improved method of recovering naphthenic acids from alkali treated mineral oils, particularly heavy bottoms or residues resulting from the vacuum distillation of alkali treated lubricating oil fractions from naphthenic crudes. Another object is to provide a method of treating such soap-oils with mineral acid whereby naphthenic acids substantially free from inorganic salt may be recovered directly from the neutralization step. A further object of the present invention is to provide a method of recovering naphthenic acids from soap-oil wherein difficulty resolvable emulsions are avoided and substantially no inorganic salt remains in the upper phase containing the naphthenic acids after the neutralization step. A still further object is to obtain a rapid and substantially complete resolution of emulsions containing liberated naphthenic acids, oil, water and inorganic salt which are formed during neutralization. An additional object is to provide a method whereby the naphthenates in soap-oils containing sulfur may be neutralized by a mineral acid without the foaming ordinarily caused by the H28 evolution. These and additional objects will be apparent from the following detailed description of our invention.

We have found that the degree of dilution of mineral acid and soap-oil during neutralization and the quantity of mineral acid with which the soap-oil may be contacted initially must be maintained within certain critical limits if difficultly resolvable emulsions are to be avoided. If the importance of either of these factors is disregarded emulsion problems are exeperienced whereas if the soap-oil is neutralized in two stages in accordance with the present invention, as will hereinafter be more fully described, substantially complete recovery of salt-free naphthenic acids may be obtained in a commercially expedient manner. It has been discovered further that the foaming caused by H23 evolution when soap-oils containing sulfur are treated may be avoided and that the admixing of soap-oil and mineral acid may be carried out in a much shorter time if the soap-oil is added to dilute mineral acid rather than adding the acid, either dilute or concentrated, to the soap-oil.

The exact nature of the emulsions which are encountered in neutralizing a soap-oil is not entirely understood but it has been found that unless a critical amount of properly diluted acid (less than the stoichiometric quantity required for total neutralization of the soap-oil) is reacted with the soap-oil in a first stage, the emulsions which form will not resolve in any reasonable time. When this critical amount of acid is initially employed, however, the emulsions resolve substantially at once and the remainder of the stoichiometric quantity may be added thereafter without further problem. Thus, for example, when dilute acid is added to soap-oil a viscous tan-colored emulsion exists as the pH is lowered until the critical amount of acid has been added, at which point the viscosity of the is immediately reduced, its color changes to black and it is apparent that the emulsion has resolved even though agitation continues. Settling of the mixture verifies this fact. On the other hand, when diluted soap-oil is added to the critical amount of dilute acid the soap oil is substantially dispersed at first while its concentration in the aqueous acid is low. When a substantial portion has been introduced, however, a stable black emulsion forms which will not resolve upon settling. This comparatively fluid emulsion exists until all of the soap-oil has been added at which time the emulsion is resolved and settling of the system results in rapid separation of substantially all of the water. Thus, the emulsions encountered in the process described herein are considered to be resolved, in accordance herewith, when the stability thereof is such that were the system permitted to settle for minutes at a temperature of at least about 189 F. at least about 80 percent of the; aqueous phase would separate. It is to be understood that the system need not be settled for emulsion resolution to occur. W hen. more or less than the hereinafter defined critical amount of acid is employed the emulsion which exists is 'not resolved and will not settle into two phases in a substantial period of time, for example 24 hours. The quantity of dilute acid which is reacted with a given amount of a soap-oil obviously aiiects the pH of the system and it is therefore apparent that the critical range of acid addition can be defined in terms of pH and some reference will hereinafter be made thereto. It is preferred, however, to describe the invention in a manner which will best define a commercial operation and since it is deemed more desirable commercially, to state that a given amount of acid should be added to insure avoidance of a difiicultly resolvable emulsion the present invention is described with particular respect thereto.

Fig. l is a graph wherein the percent water separated in 10 minutes from two different highly diluted soap-oil--sulfuric acid systems is plotted against the quantity of sulfuric acid (in terms of the percentage of the stoichiometric quantity required for neutralization of the soap-oil) employed in the neutralization. This graph clearly demonstrates the critical importance of the quantity of acid employed.

Fig; 2 is a graph wherein the percent water separated in 10 minutes from diluted soap-oilsulfuric acid systems is plotted against the strength of the mineral acid employed. The results of varying the concentration of the acid while holding the quantity of acid constant at 80 percent of the stoichiometric amountis demonstrated.

In accordance with thepresent invention substantially all of the naphthenic acids may be recovered from a soap-oil Without emulsion problems if the neutralization of the soap-oil is carried out with very dilute mineral acid (diluted to an extent hereinafter more fully described) in at least two distinct stages. In the first of these stages the soap-oil is agitated with a dilute mineral acid solution containing a critical amount of mineral acid which is between about 65 percent and about 85 percent, preferably between about 70 and about 80 percent, of the stoichiometric amount (determined by titration with mineral acid) required for total neutralization of the soap-oil. The dilute system of soap-oil and mineral acid is agitated until all ofthe mineral acid has reacted and resolution of the emulsion has occurred. At this point the aqueous phase of the system is at a'pH of from about 6 to about 8. Addition of the remainder of the stoichiometric quantity of acid may be made immediately after resolution has occurred. The fact that resolution has taken place may be readily determined, e. g. by withdrawing a sample if the mix-- point the water layer may be drawn off or agitation of both phases may be resumed and the remainder of the stoichiometric quantity of acid added either to the total system or to the more or less water-free upper layer. Once the emulsion has been resolved, addition of the remainder of the stoichiometric quantity does not create an emulsion problem. The rest of the acid is preferably added in a dilute solution but not necessarily of the same strength as initially employed. It should be understood that it is unnecessary to stop stirring to determine whether or not the emulsion has resolved since that fact may be readily determined during agitation. Contacting the soap-oil with either more than about percent or less than about 65 percent of the stoichiometric quantity of acid results in diflicultly resolvable emulsions having high inorganic salt content'whereas stepwise neutralization, in the manner set forth, results in no such problems and yields an'excellent recovery of low salt-content naphthenic acids in oil. The naphthenic acidoilmixture may then be further purified and fractionated in accordance with well-known methods. As indicated above, when the soap-oil is added to acid diluted in accordance herewith substantially no foaming occurs. as isthe case when the order of addition is reversed and the acid, dilute or concentrated, is added tothe soapoil; thus, it is preferred to add a sulfur containing soap-oil to the acid since the time required for such addition is cut to less than one-fourth that required for acid addition to soap-oil. If,

however, it is found more desirable because of certain equipment limitations, etc. to add acid to soap-oil, a foam depressant, such as lauryl alcohol or a silicone polymer, 'may advantageously be employed but even with the defoamer considerably more time is requiredfor the addition since foaming remains a' substantial problem;

When soap-oil is added to dilute acid it is preferred to reduce the viscosity of the soap-oil with a portion of the calculated amount of water, ultimately needed to give an acid strength within the hereinafter defined range, so as to permit ease of handling. The soap-oil mayof course be advantageously diluted in this manner when the reverse order of addition is employed.

Equal in importance to the quantity of acid which may be employed in the first stage of our process is the extent to which the system is diluted with water during neutralization. Stated somewhat differently, the strength of the mineral acid which is contacted with the soap-oil in the initial stage is of critical importance; and unless the acid is sufficiently dilute the use of an amount thereof within the above stated. critical limits will result in difiicultly resolvable emulsions.

Thus, it has been found that a certain minimum dilution (or maximum acid strength) must be observed in order to obtain rapid resolution of the emulsion and separation of salt and substantially all of the water from the naphthenic acids and oil. It has been found that the strength of the aqueous mineral acid during the first stage V should be no more than about 5 percent with a practical lower limit of about 1 percent. There is theoretically no actual lower limit since excessive dilution will give the desired separation but in turn results in a waste of valuable equipment capacity, which is always an important consideration. It has been found that certain characteristics of individual soap-oils will, to a considerable extent, influence the strength of acid used within this narrow range. It is postulated that the degree of dilution, or acid strength, is in some way related to the potential inorganic salt content of a particular neutralized soap-oil; such inorganic salt being readily determined by burning a sample of soap-oil in the presence of excess sulfuric acid and measuring the sulfated ash so obtained. The salt content of such soap-oils ordinarily will vary within a range of from about percent to about 20 percent by weight of the total soap-oil and we have found that the greater the potential salt content the more dilute, within the above designated range, should be the acid employed. Thus, it has been found for example, when a soap-oil having a potential salt content of 19.4 percent was treated with 80 percent of the stoichiometric quantity of sulfuric acid and settled, that an acid strength of about 1.4 percent is required to obtain separation of about 80 percent of the water in 10 minutes whereas acid of almost 4 percent strength may be employed with a soap-oil having a potential salt content of 13.4 percent to obtain the same desirable result.

The graphs shown in Figs. 1 and 2 depict, with respect to two diiferent soap-oils, the critical nature of (1) employing an amount of mineral acid within the range of from about 65 percent to about 85 percent of the stoichiometric quantity of mineral acid necessary to totally neutralize a particular soap-oil and (2) the strength of the acid which is employed, respectively. Thus, in Fig. 1 is shown the result of varying the amount of acid employed in th neutralization step in systems which are diluted to such an extent that the dilution variable is removed from consideration; and in Fig. 2 the percent acid is held constant at 80 percent while the acid strength is varied. Since the important factor in recovering the naphthenic acids from the soap-oil on a commercial basis is to obtain rapid resolution of the emulsion formed between the soap-oil and water, both the percentage acid employed and the strength of that acid are plotted against the percentage of the total water which separates in 10 minutes. 80 percent separation of the water in that period of time is considered excellent. Analyses of Soap-oil A and Soap-oil B (residual fractions from a distillation of a caustic treated lube oil fraction of a Gulf Coast crude) which were used in the tests plotted in Figs. 1 and 2 are as follows:

Soap-Oil Al Soap-Oil B Percent Percmozt HZS Available on Acidification 55 Free Caustic 0.82 0. 34 Naphthenates i. 36. 7 35. 7 Oil and Residuum 49. 9 56.3 Saponifiable 6. l 2. 6 Sulfated Ash 19. 4 13.4

ples. The temperature employed during both reaction and settling was about 200 F. in each of the examples.

Example 1 To 500 grams of Soap-oil B which had been diluted with 1000 cc. of water were added, with agitation, 46.8 grams of H2804 diluted with 250' cc. of water (the stoichiometric quantity of acid required for total neutralization of the soap-oil). Excessive amounts of foam, caused by Has evolution necessitated the addition of the acid being carried out over a period of about 4 hours. The emulsion resulting from this operation did not settle to any substantial extent in 24 hours. This necessitated steam distilling the entire emulsion including a large amount of water and sodium sulfate.

Example 2 To 500 grams of Soap-oil B diluted with 1000 cc. of water were added, with agitation, 37.4 grams of H2804 in 250 cc. of water percent of the stoichiometric quantity of acid). Excessive amounts of foam caused by Has evolution resulted in the addition of acid being carried out over a period of about 3 to 4 hours. Agitation of this mix was stopped after all of the sulfuric acid was reacted and an obvious decrease in viscosity thereof had taken place. The system was permitted to settle to give two phases the lower of which constituted approximately 60 percent of the total water present in the original system; it is estimated that about 20 percent of the water evaporated during heating. The pH of the aqueous layer was 7. The steam distillation of the upper layer resulted in about 80 percent recovery of naphthenic acids present in the form of soap in the orginial soap-oil. Substantially all of the sodium sulfate present in the reaction mixture was in the water layer and therefore it was not necessary as in Example 1 to charge the water and sodium sulfate to the steam distillation column.

Example 3 To 500 grams of Soap-oil B diluted with 500 cc. of water was added with agitation, 37.4 grams of I-IZSO4 diluted with 200 cc. of water (80 percent of the stoichiometric quantity of acid). 10 drops of lauryl alcohol were added to the system to suppress foaming and as a result the diluted acid was added in slightly over one hour. The mixture was stirred with steam at a temperature of about 215 E. which resulted in condensation of about 200 cc. of water. Resolution of the emulsion occurred and the system was settled to give a two phase system. The lower layer which had a pH of 7 comprised sodium sulfate and more than about 80 percent of the water present in the system including condensate. The aqueous layer was withdrawn, agitation of the remainder was resumed and there was then introduced thereto an additional 9.3 grams of sulfuric acid in 20 cc. of water (the remainder of the stoichiometric quantity). Steam distillation of the upper naphthenic acid-oil layer resulted in percent recovery of available naphthenic acids based upon the original soap-oil.

Example 4 A diluted sulfuric acid solution comprising 37.4 grams of H2804 (80 percent of the stoichiometric quantity of acid) in 200 cc. of water was prepared and to it were added 500 grams of Soap-oil B diluted with 500 cc. of water. The soap-oil was added rapidly over a period of about 30 minutes Example 5 A dilute acid solution comprising 37.4 grams of H2804 (80 percent of the stoichiometric quantity) and 500 cc. of water was prepared and subjected to rigorous mechanical agitation. 500

grams of Soap-oil B was emulsified with 500 cc. of water and that emulsion was introduced to the dilute acid in 20 minutes without foaming problems. An additional 250 cc. of water were added as washv and make-up for that which had evaporated. Agitation was halted and the system was permitted to settle. 940 cc. of water settled out in about minutes and were drawn oil". 9.4 grams of H2504 in solution of 5 percent concentration were then added to the remaining upper layer and agitation was resumed for a few minutes. Steam distillation of the resulting product gave substantially 100 percent recovery of available naphthenic acid in the orginial soap-oil.

Since the neutralization of the naphthenates in the above described dilution takes place very slowly and is essentially incomplete at tempera- .tures below about 180 F. it is necessary to operate at temperatures thereabove, preferably of at least about 195 F. The settling step is preferably conducted at an elevated temperature in order to' promote stratification.

A soap-oil is totally neutralized in accordance herewith when all of its alkaline constituents have been reacted with a mineral acid. At this point the pH of the system is in the range of from about 3 to about 5 due to liberated naphthenic acids.

Any of the strong mineral acids, e. g. sulfuric, hydrochloric, or phosphoric may be employed in accordance herewith but it is preferred to operate with sulfuric acid because of its availability and greater freedom from corrosion difiiculties. ,Since'the acid is used in such dilute solutions it is apparent that any of the various commercial strengths of acid or even waste acid may be employed. Percentages of mineral acid referred to herein are by weight based on 100 percent acid. The acid strengths given are based upon the weights of mineral acid and total water present in the soap-oilmineral acid system.

'We claim:

1. A method of treating a naphthenate containing residue resulting from the distillation of an'alkali treated petroleum oil which comprises contacting said residue at a temperature of at least about 180 F. with an amount from about 675 percent to about 85 percent of the stoichiometric quantity of mineral acid required to totally neutralize said residue, said mineral acid being in a concentration of no greater than about 1 percent, agitating the mixture of dilute mineral acid and residue at'said temperature until emulsion resolution has taken place, adding the remainder of said stoichiometric quantity of mineral acid with agitation at said temperature after -said resolution has taken place, settling said mix- 8 :ture to permit substantially complete separation of water and inorganicsalt and recovering the substantially salt freeupper layer.

2. The method of claim 1 wherein the mineral acid employed is sulfuric acid.

3. The method of treating a naphthenatecontaining residue resulting from the distillation of alkali treated petroleum oil which method comprises admixing said residue with an amount of from about '70 to about percent of the'stoichiometric quantity of 'mineral acid required to totally neutralize said residue and an amount of water suflicient to result in a mineral acid'concentration of from about 1 percent to about 5 percent, agitating the mixture of mineral acid, water, and residue until all of said'mineral acid has been reacted and emulsion resolution has oc curred, adding the remainder of the stoichiometric quantity of mineral acid with agitation after emulsion resolution has occurred, settling said mixture to permit separation ofwater and salt present therein and recovering the upper-oil and naphthenic acid containing layer.

4. The method of claim 3 wherein the mineral acid employed is sulfuric acid.

5. The method of treating a naphthenate containing residue resulting from the distillation of an alkali treated petroleum oil which comprises introducing said residue to a mineral acid solu- 7 tion containing an amount of from about 65 to about percent of the stoichiometric quantity of mineral acid required to totally neutralize said residue in a concentration of from about '1 percent to about 5 percent, agitating the mixtureof dilute mineral acid and residue until all of said mineral acid has been reacted and emulsion resolution has occurred, adding the remainder of said stoichiometric quantity of mineral acid with agitation after said emulsion resolution has occurred, settling said mixture to permit separation of water and inorganic salt present therein and recovering the substantially salt-free oil andnaphthenic acid containing layer.

6. The, method of claim 5 wherein thetreatment of the naphthenate containing residue takes place at a temperature of at least about F.

'7. The method of claim 5 wherein the mineral acid is sulfuric acid.

8. The method of treating a sulfur bearing, naphthenate containing residue resulting from the distillation of an alkali treated petroleum oil which method comprises emulsifying said residue with sufficient water to reduce its viscosity at about 180 F. to a point where it may be poured, introducing the resulting emulsion of ,residueand water to a sulfuric acid solution comprising an amount of from about '70 percent to about .80 percent of the stoichiometric quantity of sulfuric acid required to totally neutralize said residue and at least sufficient water when combined with the water emulsified with said residue to result in a sulfuric acid concentration of from about 1 percent to about 5 percent, agitating the mixture of sulfuric acid, water, and residue until emulsion resolution takes place, adding the remainder of the stoichiometric quantity of sulfuric acid in a dilute solution with agitation after said emulsion resolution has taken place, settling said mixture to permit separation of substantially all of the water and inorganic salt and recovering the substantially salt-free 'oil and naphthenic acid containing layer.

9. The method of claim 8 wherein the treatment of the naphthenate containing residue takes place at a temperature of at least about 180 F.

10. The method of treating naphthenate containing residues resulting from the distillation of an alkali treated petroleum oil which comprises introducing to such a residue a mineral acid solution comprising an amount of from about 65 percent to about 85 percent of the stoichiometric quantity of mineral acid required for total neutralization of said residue, said mineral acid being in a concentration of from about 1 percent to about 5 percent, agitating the mixture of mineral acid, Water, and residue until emulsion resolution has taken place, adding the remainder of said stoichiometric quantity of mineral acid after emulsion resolution has taken place, settling said mixture to permit separation of substantially all of said Water and inorganic salt and recovering the substantially salt-free upper layer comprising oil and naphthenic acids.

11. The method of claim wherein the mineral acid is sulfuric acid.

12. The method of claim 10 wherein the treatment of the naphthenate containing residue is carried out at a temperature of at least about 180 F.

13. The method of claim 10 wherein a foam depressant is added when the residue contains sulfur.

14. The method of treating naphthenate containing residues resulting from the distillation of alkali treated petroleum oils which comprises contacting said oil with an amount of from about percent to about percent of the stoichiometric quantity of mineral acid required to totally neutralize said residue, said mineral acid being in a concentration of from about 1 percent to about 5 percent, agitating the mixture until emulsion resolution occurs, settling said mixture to permit substantially all of the water and inorganic salt to separate, as a lower layer, withdrawing said lower layer, admixing the remainder of said stoichiometric quantity of mineral acid in dilute solution to the remaining upper layer, agitating the admixture and recovering the substantially salt-free mixture of oil and naphthenic acids.

15. The method of claim 14 wherein the mineral acid is sulfuric acid.

15. The method of claim 14 wherein the treatment of the naphthenate containing residue is carried out at a temperature of at least about F.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,802,336 Cook Apr. 28, 1931 2,035,742 Ewing Mar. 31, 1936 2,133,766 Ewing Oct. 18, 1938 2,170,506 Reiber Aug. 22, 1939 2,220,013 Bruun Oct. 29, 1940 2,537,576 Dunlap Jan. 9, 1951 

5. THE METHOD OF TREATING A NAPHTHENATE CONTAINING RESIDUE RESULTING FROM THE DISTILLATION OF AN ALKALI TREATED PETROLEUM OIL WHICH COMPRISES INTRODUCING SAID RESIDUE TO A MINERAL ACID SOLUTION CONTAINING AN AMOUNT OF FROM ABOUT 65 TO ABOUT 85 PERCENT OF THE STOICHOIMETRIC QUANTITY OF MINERAL ACID REQUIRED TO TOTALLY NEUTRALIZE SAID RESIDUE IN A CONCENTRATION OF FROM ABOUT 1 PERCENT TO ABOUT 5 PERCENT, AGITATING THE MIXTURE OF DILUTE MINERAL ACID AND RESIDUE UNTIL ALL OF SAID MINERAL ACID HAS BEEN REACTED AND EMULSION RESOLUTION HAS OCCURRED, ADDING THE REMAINDER OF SAID STOICHIMETRIC QUANTITY OF MINERAL ACID WITH AGITATION AFTER SAID EMULSION RESOLUTION HAS OCCURRED, SETTLING SAID MIXTURE TO PERMIT SEPARATION OF WATER AND INORGANIC SALT PERSENT THEREIN AND RECOVERING THE SUBSTANTIALLY SALT-FREE OIL AND NAPHTHENIC ACID CONTAINING LAYER. 